1. Filed of the Invention
The present invention relates to a method of manufacturing a disk, such as a DVD, and more particularly, to a technical field pertaining to a method of manufacturing a disk by means of bonding together substrates, each having formed therein pits and grooves carrying recorded information.
2. Description of the Related Art
Demand for a further improvement in recording density has recently existed for disks such as DVDs, and attention has been paid to a multilayer disk having a bonded structure of information recording surfaces of disks. For example, in case of a two-layer disk, two substrates for bonding purpose, each having an information recording surface, are manufactured separately. An intermediate bonding layer made of an adhesive is provided on one of the substrates which remains stationary. The other substrate is aligned and stacked onto the intermediate bonding layer, thereby constituting a two-layer disk. In connection with such a two-layer disk, information can be recorded on either layer of a single disk, and the thus-recorded information can be read selectively, as required. Hence, the recording capacity of a disk can be increased.
An increase in the numerical aperture of an optical system for further improving recording density has been under review. In this case, a focal length to a recording layer in the two-layer disk becomes smaller, and hence the substrates to be bonded assume an ultra-small thickness on the order of 100 xcexcm. When such thin substrates are bonded together, accurate alignment of the substrates is not easy. Since substrates are thin and have insufficient rigidity, the substrates become prone to nonuniform deformation or warpage during alignment. Thus, sustaining bonded surfaces flat becomes difficult, thereby posing a higher risk of the substrates being bonded together with eccentricity or positional misalignment arising in a part of the substrates.
The present invention has been conceived to solve the problem and is aimed at providing a disk manufacturing method which enables manufacture of a multilayer disk with superior positional accuracy while preventing occurrence of deformation or warpage, maintaining flat bonded surfaces, and preventing occurrence of eccentricity or positional misalignment even when very thin substrates of insufficient rigidity are bonded together.
In order to solve the problem, according to a first aspect of the invention, there is provided a disk manufacturing method for manufacturing a disk having a laminated structure, comprising the steps of:
fixing a reinforcement substrate for reinforcing a first substrate onto the first substrate acting as one layer of the disk;
aligning the first substrate fixed to the reinforcement substrate to a second substrate serving as another layer of the disk;
bonding the first substrate fixed to the reinforcement substrate to the second substrate through an intermediate adhesive layer; and
separating the reinforcement substrate from the first substrate.
According to the invention, when there is manufactured the disk having the laminated structure, since the reinforcement substrate is integrally fixed to the first substrate in the fixing step, even if the first substrate has a small thickness, stiffness is ensured to prevent occurrence of deformation or warpage. In the aligning step and the bonding step, the reinforced first substrate is aligned with the second substrate to bond them together through the intermediate adhesive layer. In the separating step, the reinforcement substrate is separated from the first substrate after the first substrate and the second substrate have been bonded together. Accordingly, a bonded surface is maintained to be smooth by the reinforcement substrate, thereby ensuring a high degree of positional accuracy. Occurrence of positional misalignment and eccentricity is prevented, thereby enabling accurate bonding of disks.
According to a second aspect of the invention, there is provided the disk manufacturing method according to the first aspect of the invention, further comprising the steps of:
aligning the first substrate to a stamper having a pit pattern; and
transferring the pit pattern onto the first surface.
According to the invention, when the disk having the laminated structure is manufactured, in the fixing step, the stiffness of the first substrate is ensured to prevent occurrence of deformation or warpage and in the aligning and bonding steps, occurrence of positional displacement and eccentricity can be prevented as well as the first aspect of the invention. In addition, in the transferring step, the pit pattern is transferred to the reinforced first substrate by using the stamper. Accordingly, the pit pattern formed on the first substrate in the transferring step is accurately aligned by the reinforcement substrate. Hence, positional accuracy of an information recording surface on another layer of the disk having the laminated structure can be ensured.
According to a third aspect of the invention, there is provided the disk manufacturing method according to the second aspect of the invention, wherein the aligning step of aligning the first substrate to the stamper, the transferring step, and the other steps are performed in this order.
According to the invention, when the disk having the laminated structure is manufactured, the pit pattern is transferred onto the first substrate by using the stamper before the first substrate is reinforced. Subsequently, the fixing step, the aligning step, and the bonding step are performed as well as the first and second aspects of the invention to ensure the stiffness of the first substrate and preventing occurrence of positional misalignment and eccentricity of disks. Accordingly, even when an information recording surface (the pit pattern) has already been transferred onto the first substrate at manufacturing the disk, the first substrate is reinforced by using the reinforcement substrate to bond disks. Hence, there can be ensured positional accuracy of a disk having a laminated structure as well as the first and second aspects of the invention.
According to a fourth aspect of the invention, there is provided the disk manufacturing method according to any one of the first to third aspects of the invention,
wherein the fixing step fixes the reinforcement substrate to the first substrate through an adhesive layer; and
the separating step separates the reinforcement substrate from the first substrate by reducing adhesive strength of the adhesive layer.
According to the invention, in the fixing step, the reinforcement substrate is integrally bonded to the first substrate through the adhesive layer. In the separating step, the adhesive strength of an adhesive layer is reduced to separate the reinforcement substrate from the first substrate. Hence, use of an adhesive sheet whose adhesive strength reduces at temperature or upon exposure to UV rays or use of electrostatic electricity enables easy fixing and separation of the first substrate to and from a substrate having high stiffness.
According to a fifth aspect of the invention, there is provided the disk manufacturing method according to any one of the first to third aspects of the invention,
wherein the fixing step uses a fixing member to fix the reinforcement substrate to the first substrate; and
the separating step removes the fixing member to separate the reinforcement substrate from the first substrate.
According to the invention, in the fixing step, the first substrate is integrally bonded to the reinforcement substrate by the fixing member. In the separating step, the fixing member is removed to separate the reinforcement substrate from the first substrate. Accordingly, a fixing member having a structure for pressing the first substrate to a substrate having high rigidity in a state where the substrate closely contact with the first substrate, the fixing member is attached, and whereby it can be easily performed to fix and separate the first substrate to and from the substrate having high rigidity.
According to a sixth aspect of the invention, there is provided the disk manufacturing method according to any one of the first to third aspects of the invention, wherein the reinforcement substrate has higher rigidity than the first substrate.
According to the invention, in the fixing step, a substrate having high rigidity is integrally fixed to the first substrate. Hence, the first substrate can be sufficiently reinforced by, for example, glass substrate which is thicker than the first substrate and sufficiently assure rigidity, and positional accuracy in the bonding and transferring steps can be improved further.
According to a seventh aspect of the invention, there is provided the disk manufacturing method according to any one of the first to third aspects of the invention, wherein the alignment step aligns the first substrate fixed to the reinforcement substrate to the second substrate in relation to a peripheral direction of the first substrate fixed to the reinforcement substrate.
According to the invention, in the bonding step, the first and second substrates are aligned with each other in relation to the peripheral direction of the first substrate fixed to the reinforcement substrate. Hence, two layers of disks in which conditions of recording areas depending on peripheral directions of the disks are different from each other can be accurately aligned with each other.
According to a eighth aspect of the invention, there is provided the disk manufacturing method according to the second aspect of the invention, wherein the alignment step uses a center and peripheral portion of the first substrate fixed to the reinforcement substrate as reference positions to align the first substrate fixed to the reinforcement substrate to the second substrate.
According to the invention, since a center of a disk and a peripheral portion of a disk are used as the reference positions for alignment, positions of the centers of the disks and positions in peripheral directions of the disks in a two-layer disk can be accurately aligned respectively.
According to a ninth aspect of the invention, there is provided the disk manufacturing method according to the seventh aspect of the invention, wherein the alignment step uses a plurality of peripheral portions of the reinforcement substrate as reference positions to align the first substrate fixed to the reinforcement substrate to the second substrate.
According to the invention, the plurality of the peripheral portions of the disk are used as the reference positions when aligning in relation to the peripheral direction of the disk. Hence, each of positions of overall areas on the two-layer disk can be accurately aligned.
According to a tenth aspect of the invention, there is provided a disk transfer method comprising the steps of:
fixing a reinforcement substrate for reinforcing a first substrate onto the first substrate acting as one layer of the disk;
aligning the first substrate to a stamper having a pit pattern;
transferring the pit pattern onto the first substrate; and
separating the reinforcement substrate from the first substrate.
According to the invention, in case that the pit pattern is transferred onto a disk having laminated structure, in the fixing step, the stiffness of the first embodiment can be ensured as well as the invention on the disk manufacturing method. In the transferring step, the pit pattern is transferred onto the reinforced first substrate by using the stamper. Hence, a high degree of positional accuracy of a pit pattern or the like formed on the first substrate in the transferring step can maintained.